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list p=16C84,t=ON,c=132,n=80,st=off include "P16C84.INC" cblock 0x0C temp x,y,a x1,y1,cnt result endc ORG 0 ;Reset Vector GOTO Main ORG 4 ;Interrupt Vector Main CLRF x clrf x1 movlw 0x30 movwf y1 movwf x1 l1 movf y1,w movwf y movlw 3 addwf x1,w movwf x1 movwf x CALL FRAC_DIV movf a,w movwf x CALL arctan goto l1 FRAC_DIV: ;------------------- ;Fractional division ; ; Given x,y this routine finds: ; a = 256 * y / x ; movlw 8 ;number of bits in the result movwf cnt clrf a ; the result movf x,w L1: clrc rlf y,f ;if msb of y is set we know x<y rlf a,f ;and that the lsb of 'a' should be set subwf y,f ;But we still need to subtract the ;divisor from the dividend just in ;case y is less than 256. skpnc ;If y>x, but y<256 bsf a,0 ; we still need to set a:0 btfss a,0 ;If y<x then we shouldn't have addwf y,f ;done the subtraction decfsz cnt,f goto L1 return ;---------------------------------------------------------- ; ;arctan (as adapted from the similar arcsin function) ; ; The purpose of this routine is to take the arctan of an ;8-bit number that ranges from 0 < x < 255/256. In other ;words, the input, x, is an unsigned fraction whose implicit ;divisor is 256. ; The output is in a conveniently awkward format of binary ;radians (brads?). The output corresponds to the range of zero ;to pi/4 for the normal arctan function. Specifically, this ;algorithm computes: ; ; arctan(x) = real_arctan(x/256) * 256 / (pi/4) ; for 0 <= x <= 255 ; ; where, real_arctan returns the real arctan of its argument ;in radians. ; ; The algorithm is a table look-up algorithm plus first order ;linear interpolation. The psuedo code is: ; ;unsigned char arctan(unsigned char x) ;{ ; unsigned char i; ; ; i = x >> 4; ; return(arctan[i] + ((arctan[i+1] - arctan[i]) * (x & 0xf))/16); ;} ; ; arctan SWAPF x,W ANDLW 0xf ADDLW 1 MOVWF temp ;Temporarily store the index CALL arc_tan_table ;Get a2=atan( (x>>4) + 1) MOVWF result ;Store temporarily in result DECF temp,W ;Get the saved index CALL arc_tan_table ;Get a1=atan( (x>>4) ) SUBWF result,W ;W=a2-a1, This is always positive. SUBWF result,F ;a1 = a1 - (a1-W) = W CLRF temp ;Clear the product CLRC BTFSC x,0 ADDWF temp,F RRF temp,F CLRC BTFSC x,1 ADDWF temp,F RRF temp,F CLRC BTFSC x,2 ADDWF temp,F RRF temp,F CLRC BTFSC x,3 ADDWF temp,F RRF temp,W ADDWF result,F RETURN arc_tan_table ADDWF PCL,F RETLW 0 RETLW 20 ;atan(1/16) = 3.576deg * 256/45 RETLW 41 RETLW 60 RETLW 80 RETLW 99 RETLW 117 RETLW 134 RETLW 151 RETLW 167 RETLW 182 RETLW 196 RETLW 210 RETLW 222 RETLW 234 RETLW 245 RETLW 0;atan(32/32) = 45deg * 256/45 END |